Certain internal combustion engines utilize a compression device such as a turbocharger to increase engine torque/power output density. In one example, a turbocharger may include a compressor and a turbine connected by a drive shaft, where the turbine is coupled to an exhaust manifold side and the compressor is coupled to an intake manifold side of an engine. In this way, the exhaust-driven turbine supplies energy to the compressor to increase the pressure (e.g. boost, or boost pressure) in the intake manifold and to increase the flow of air into the engine. The boost may be controlled by adjusting the amount of gas reaching the turbine, for example with a wastegate. A spring loaded wastegate valve may be controlled based on operating conditions to achieve the desired boost. The spring of the wastegate valve may be degraded over time causing the wastegate valve to be stuck in an at least partially open position. A partially stuck open wastegate valve may reduce boost pressure and adversely affect engine emissions.
One example approach for diagnosing wastegate valve operation is shown by Propernick in U.S. Patent Application No. 20020148224. Diagnostics of components of a turbocharger including a wastegate valve may be carried out during engine-off conditions. Pressurized air from a source may be delivered to the turbocharger and air pressure within the turbocharger may be estimated via a pressure gauge. Any leaks in the turbocharger system, including the wastegate valve may be detected under the applied pressure.
However, the inventors herein have recognized potential issues with such systems. As one example, additional components including an air supply source, conduits for air supply, and one or more pressure gauges may be required to carry out the diagnostics of the wastegate, thereby adding to costs and packaging concerns.
In one example, the issues described above may be addressed by an engine method comprising: testing for degradation of a wastegate valve, positioned in a wastegate passage which is coupled in parallel to a turbine positioned in an exhaust system of an engine, by routing airflow from the exhaust system through the wastegate valve into an intake of the engine and comparing the airflow in the intake to a baseline airflow through the wastegate valve into the engine intake. In this way, by routing ambient air through the wastegate valve during vehicle key-off conditions, it is possible to detect degradation of the wastegate valve.
In one example, a diagnostic routine of the wastegate valve may be opportunistically carried out during vehicle key-off conditions when the engine is not operated. The engine may be a boosted engine comprising a turbine driven intake air compressor and an electrically driven intake air compressor (herein also referred to as a battery operated electric booster) that is selectively operated for providing additional boost during increased torque demand. During a vehicle-off condition, the wastegate valve may be in a default closed condition. The engine may be reverse rotated, unfueled, and also the electric booster is reverse rotated to draw in ambient air from the tailpipe and route the air to the intake manifold via the exhaust turbine. The intake airflow may be estimated via a manifold airflow sensor and compared to a baseline airflow. Upon installation of the wastegate valve, the baseline air flow may be obtained by reverse rotating the engine, reverse rotating the electric booster, and estimating air flow through the intake manifold via the MAF sensor. The wastegate valve may be diagnosed to be stuck in at least a partially open position responsive to the intake airflow being higher than the baseline airflow. A degree of opening of the wastegate valve may be estimated based on a difference between the intake airflow and the baseline airflow, the degree of opening increasing with an increase in the difference between the intake airflow and the baseline airflow. Upon detection of degradation of the wastegate valve, during an immediately subsequent engine operation, the electric booster operation may be adjusted to account for the loss in boost pressure due to undesired exhaust flow via the degraded wastegate valve.
In this way, by opportunistically using existing engine components, such as an electric booster and a manifold air flow sensor, the need for additional sensors and/or equipment for diagnostics of a wastegate valve may be reduced or eliminated. By reverse rotating the engine, the drop in exhaust pressure may be utilized to draw in ambient air and carry out wastegate diagnostics. The technical effect of flowing air through the turbocharger during engine non-combusting condition is that it is possible to determine an amount of opening of the degraded wastegate valve based on the comparison between the intake airflow and the baseline airflow. By identifying degradation of the wastegate valve, suitable mitigating steps may be taken during subsequent engine cycles to improve engine performance. Overall, by regularly monitoring the health of the wastegate valve, fuel efficiency and emissions quality may be improved.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.